Magnesium antimonate phosphor



2,865,862 MAGNESIUM ANTIMONATE PHOSPHOR Richard W. Mooney, Towanda, Pa.,assignor to Sylvania Electric Products Inc., Salem, Mass., a corporationof Massachusetts No Drawing. Application October 24, 1956 Serial No.617,905 2 Claims. (Cl. 252--301.5)

This invention relates to magnesium lithium antimonate phosphors.

Such phosphors activated by either manganese or uranium, or both, havebeen previously known, as shown in U. S. patent application Serial No.319,188, filed November 6, 1952, by' Peter W. Ranby, now Patent No.2,785,137 issued Mar. 12, 1957, but their fluorescent emission was inthe green to red region of the spectrum.

I have now discovered that the emission can be shifted to the blue byreplacing the manganese and uranium activators by tungsten or titanium.

In addition, I have found that the use of titanium as a secondaryactivator, with manganese or uranium as the other activator, willgreatly increase the light emission over that obtained with activationby manganese or uranium alone.

The proportion by weight of magnesium, lithium and antimony, expressedas the oxides, in the phosphor, can be between 20% and 60% of magnesiumoxide (MgO), between 5% and 35% of lithium oxide (Li O), and between 30%and 70% of antimony trioxide (Sb O I prefer, however, to use between 25and 40% mag nesium oxide, between and 20% lithium oxide and between 45%and 60% antimony trioxide.

In the preparation of these phosphors, I prefer to use basic magnesiumcarbonate, lithium carbonate and antimony trioxidc as the raw materials.However, substitutions of other raw materials will give substantiallythe same results, these substitutions being obvious to those skilled inthe art. Thus, for example, magnesium oxide or magnesium hydroxide maybe used in place of the basic magnesium carbonate and similarly lithiumoxide or lithium hydroxide may be used in place of the lithiumcarbonate.

The concentration of the titanium or tungsten activators may vary over aconsiderable range from 0.0001 to 0.25 gram atoms of activator per 100grams of combined oxides in the original mixture. Preferably however thebest phosphors are obtained with titanium concentrations between 0.005and 0.04 gram atoms per 100 grams of combined oxides and with tungstenconcentrations between 0.001 and 0.02 gram atoms per 100 grams ofcombined oxides. I prefer, for convenience, to use titanium dioxide orhydrated tungsten trioxide but halides or sulphates may also beemployed. The eflect of titanium activator concentration for a specificmatrix composition is shown by way of example in Table I.

TABLE I Effect of titanium concentration [Matrix composition: MgO, 35%;L120, and SbaOs, 50%

nited States Patent" 0 The efiect of tungsten activator concentrationfor a Specific matrix composition is shown by way of example in- TableII.

TABLE II Efiect of tungsten concentration [Matrix composition: MgO, 35%;L120, 15%; and SbzOs, 50% by weight Relative Brightness [or p FinalFiring Temp. 0i- Gi'amMQleSOtWOgHzO 2,050 F. 2;2oo F.

16 22 0,0002... 33 L 33 3s 30 25 31 2s 21 i 21 The optimum firingtemperature depends upon the activator concentration as shown in TablesI and II and to some extent on the composition of the matrix.Compositions which are high in antimony trioxide or lithium oxide giveharder products and therefore require lower firing temperatures.However, I have found that the range from 1800 to 2200 F. issatisfactory for most compositions.

While: a single firing of the well mixed raw materials gives a usefulphosphor, the output is generally increased by dry grinding the product,mixing well and firing a second time. It is not necessary to employ thesame temperature for both firings and, in fact, I prefer to use atemperature of about 1800 to 2000 F. for the first firing and then toretire at a higher temperature.

If the magnesium lithium antimonate phosphor is doubly activated bytitanium and manganese the red output of the manganese-only-activatedphosphor is increased as shown by the data on Table III.

TABLE III Red response of Mn and (Mn+Ti)-activated antimonates The Mnwas present to the extent of about 0.1% by weight of the phosphor in theabove table, and the titanium was present to the extent of about 2% onthe same basis. The firing procedure is as previously described.

Titanium will also act as a secondary activator in the uranium-activatedmagnesium lithium antimonate phosphor resulting in a net increase in theemission in the green. For example a phosphor prepared with 1.0 gram ofuranyl nitrate and 1.0 gram of titanium dioxide with 50 grams ofcombined oxides is approximately 19% brighter in the green than the samephosphor without TiO The uranium was present to the extent of about 2%by weight of the phosphor and the titanium to the extent of about 2% onthe same basis. The firing procedure is as previously described.

Having shown the scope of my invention, I will now describe specificexamples of the preparation of these phosphors.

Ex. 1.-A phosphor was prepared for which the matrix has the composition:MgO, 0.563 gram moles; Li O,

0.326 gram moles; Sb 0.111 grammoles and in which the titanium activatorconcentration is 0.0162 gram atoms per 1.0 gram moles of combinedoxides. Raw materials as listed below were carefully weighed, using thehighest purity materials commercially available.

Basic magnesium car- I bonate 80.7 grams (assay 43.3% MgO) Lithiumcarbonate 37.0 grams (assay 40.5% Li O) Antimony trioxide 50.0 grams(assay 100% 513 0 Titanium dioxide 2.0 grams (assay 100% TiO Basicmagnesium carbonate 80.7 grams (assay 43.3% Mg()) Lithium carbonate 37.0grams (assay 40.5 Li O) Antimony trioxide 50.0 grams (assay 100% Sb O "Iungstic acid 1.0 gram (assay 91.9% W0 These materials were dry mixed bytumbling and then transferred to fusedsilica crucibles and fired for 1hour at 1950 F. The product was crushed after cooling,

well mixed and after transfer to a silica crucible fired again for 1hour at 2150 F.

What I claim is:

1. A phosphor comprising magnesium lithium antimonate activated by asubstance selected from the group consisting of tungsten and titanium,the selected substance being present in an amount between about 0.0001and about 0.25 gram-atoms per 100 grams of the magnesium, lithium andantimony expressed in terms of the oxides, the proportion by weight ofmagnesium, lithium and antimony, expressed as the oxides can be between20% and 60% of MgO, between 5% and of lithium oxide, and between 30% and70% of antimony trioxide, by weight.

2. A phosphor comprising magnesium lithium antimonate activated by 'asubstance selected from the group consisting of manganese and uranium,and activated also, per 100 grams of magnesium, lithium and antimonyexpressed in terms of the oxides, by between about 0.001 and 0.25gram-atoms of titanium, the proportion by weight of magnesium, lithiumand antimony expressed as the oxides can be between 20% and of MgO,between 5% and 35% of lithium oxide, and between 30% and of antimonytrioxide, by weight.

' References Cited in the file of this patent UNITED STATES PATENTSRanby Mar. 12, 1957 OTHER REFERENCES Kroger: Some Aspects of theLuminescence of Solids (1948), pp. 158-161.

1. A PHOSPHOR COMPRISING MAGNESIUM LITHIUM ANTIMONATE ACTIVATED BY ASUBSTANCE SELECTED FROM THE GROUP CONSISTING OF TUNGSTEN AND TITANIUM,THE SELECTED SUBSTANCE BEING PRESENT IN AN AMOUNT BETWEEN ABOUT 0.0001AND ABOUT 0.25 GRAM-ATOMS PER 100 GRAMS OF THE MAGNESIUM, LITHIUM ANDANTIOMNY EXPRESSED IN TERMS OF THE OXIDES, THE PROPORTION BY WEIGHT OFMAGNESIUM, LITHIUM AND ANTIMONY, EXPRESSED AS THE OXIDES CAN BE BETWEEN20% AND 60% OF MGO, BETWEEN 5% AND 35% OF LITHIUM OXIDE, AND BETWEEN 30%AND 70% OF ANTIMONY BRIOXIDE, BY WEIGHT.